3T seatpost DI2 battery holder
I bought this battery holder as it was to fit a 3T seat post 27.2. To get it in I had to crimp it with a pair of grips as I couldn't get it into he seat post. It's certainly not going to come out in a hurry that's for sure. On the plus side, it is very secure and I can remove the battery easily via the circlip.
25 August 2016

Not fit for purpose.
This arrived in a sealed bag but didn't contain a circlip or any other method of securing the battery into the metal holder. Basically useless.
04 September 2015

Cheap, Simple and Effective
This worked perfectly with my 3T Ionic seatpost. Simple push fit and battery is secure in seatpost. I have not experienced any rattles despite hitting a few potholes. Not sure how I would get it out if I ever needed to but can't think why I would need to!
21 November 2014

Does that it says on the tin
Holds battery perfectly and easy to fit.
Apparently this review was too short - but there is nothing else to say really!
27 October 2014

Just works
Will work perfectly in your 3T seatpost. Nothing else to say.
07 May 2014